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 Post subject: In Rush Current Limiter HELP Choosing
PostPosted: Apr Thu 20, 2017 11:45 pm 
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Location: Wilmington, NC 28412 USA
I have a Model 304 Pilot Radio 11 tubes 6 # 44 Pilot Lamps
Fused @ 2A on each leg
No Transformer Crazy Filament string

Using 115 VAC as Line when I first turn on the set the Lamp Voltage jumps to 14 VAC slowly drops to 5.4 Volts when stable

Would a Current limiter solve this problem ?

If so which should I use ? CL90 @ 2A or the CL 80 @ 3A

Never tried these before.

Input welcome

Thanks
Bob T


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Last edited by joybird on Apr Fri 21, 2017 9:47 pm, edited 2 times in total.
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 Post subject: Re: In Rush Current Limiter
PostPosted: Apr Fri 21, 2017 1:21 am 
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Location: Santa Rosa, CA
Really crazy circuit. Took me a long time to find the pilot lamps.

Sounds like the tube filaments are cold; the resistance is low. Then they warm up and drop more voltage, so the pilot lamp voltage changes.

Seems like that's the way it was designed. Is it blowing lamps?

Rich


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 Post subject: Re: In Rush Current Limiter
PostPosted: Apr Fri 21, 2017 2:33 am 
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Location: Tucson, Arizona U.S.A.
There are several rules for effective use of inrush limiters. Make sure they are suitable for the voltage you are applying to them. Don't use them at less than 1/4 of their rated maximum current. Use the one with the highest cold resistance that meets the other requirements. They get very hot in operation; don't locate them where they will harm other components. If you have a choice of types with suitable characteristics, the physically largest one will warm up the slowest and give the best protection.

Used correctly, they can be very effective.

Don't limit your search to the CL series; Ametherm has some interesting parts that are also widely available.

_________________
Jim Mueller


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 Post subject: Re: In Rush Current Limiter
PostPosted: Apr Fri 21, 2017 1:10 pm 
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Location: Wilmington, NC 28412 USA
Thank You

I will take your suggestions into account in choosing.

The Radio @ turn on @ 115 VAC draws 1.2 Amps settles down to .8 Amps running.
So would I be OK going with the CL90 2A or the CL80 3A?
I like the idea of the larger size. Would the heat be the same small or large?
Will Google the Ametherm. Any suggestions on that?
http://www.newark.com/ametherm/sl22-0r7 ... dp/72J6815
Very confusing to me as to ratings. Above one rated 12A so 1/4 of that is 3A. My MAX is 1.2A Would this one be suitable for the Radio?
115 VAC Max current Draw at turn on 1.2A running current .8A.

Must be many Radio collectors here that have used them. Suggestion ????>

Thanks for input

Bob T


Last edited by joybird on Apr Fri 21, 2017 6:19 pm, edited 2 times in total.

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 Post subject: Re: In Rush Current Limiter
PostPosted: Apr Fri 21, 2017 1:30 pm 
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Rich, W3HWJ wrote:
Really crazy circuit. Took me a long time to find the pilot lamps.

Sounds like the tube filaments are cold; the resistance is low. Then they warm up and drop more voltage, so the pilot lamp voltage changes.

Seems like that's the way it was designed. Is it blowing lamps?

Rich

YES Crazy Filament String. Yes @ 115 VAC it will blow 47 bulbs. Schematic insists on using #44 so put them in.
At Start up WOW do they get bright (12VAC seen) I am sure they would blow more easy if a Hot restart was done.
(QUICK OFF/ON) I have been careful bringing up Line Voltage with Variac.

Also as Bulbs blow output changes, the more Bulbs out the more it effects the output of Radio
Crazy Design for sure.
Not easy to replace Lamps Chassis must be pulled and Dial removed to access Bulbs 6 of them.

Bob T


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Fri 21, 2017 2:49 pm 
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I'd go with something like these... Radio draws less than 1A operating so they'd be fine...

For under $9 shipped, you'll have eight of them...

http://www.ebay.com/itm/8pcs-AMETHERM-C ... sZwsSzR2hQ


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Fri 21, 2017 7:32 pm 
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Called Ametherm and spoke with their Engineer
Explained what I wanted to do in regard to Antique Tube Radio with the specs in above post.

He recommend this to accomplish the task and will work well on Radio's drawing 3A or less.
It does get HOT so must be mounted in safe place.

P/N SL10 10003


Resistance at 25ºC 10 Ω ± 20 % Cold Resistance
Max Steady State Current 3 A
Max Rec Energy Rating 17 J
Actual Failure Instantaneous Energy 35 J
Dissipation Constant 11 mW/ºC
Body Temperature at 100% Max Current 151 ºC 300 Degrees F
Thermal Time Constant 30 sec
Max Cap at 277V 220μf
Material Type C

Ordered 10 from Mouser to try out. Not sure I like 300 degrees at max current I believe that is with 3Amp draw so less at .7 amp still I figure that is Warm . Won't know til I try.

Bob T.


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Fri 21, 2017 8:38 pm 
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With only 10 ohms at 25C, I doubt you'll see enough reduction in surge to be noticeable...

The tube sets that used surge protection in tube string were often in the 500 ohm range & why I recommended(and still do) the 220 ohm units...


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Fri 21, 2017 9:28 pm 
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35Z5 wrote:
With only 10 ohms at 25C, I doubt you'll see enough reduction in surge to be noticeable...

The tube sets that used surge protection in tube string were often in the 500 ohm range & why I recommended(and still do) the 220 ohm units...


Point well taken Thank you for that.

I was going through a Parts Box I had stripped off the Radio 4 years ago . I must have been thinking surge back then as I just found some Current limiters I bought from Mouser back in 2013 .
I have (5) 1.1A 50 ohm Small Disc Mouser 527-CL140
(5) 2A 120 ohm Large Disc Mouser 527-CL90
Yes I would think the engineer I spoke with would have know better. I supplied all the info he wanted.
after all the Company makes these things , they should be more helpful.
I will try all 3 and see what result I get. Report back.
I truly appreciate your help here

Thank You
Bob T


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Fri 21, 2017 10:02 pm 
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I installed the 2A 120 ohm

A cold start the Filament to the Lamps is now 11 Volts so it only dropped 3 volts (14 VAC peak)

I figure the cold filament resistance on this chassis is around 200 ohms 11 tubes and 6 #44 Lamps.

Ordered the suggested 1A 220 Ohm Limiters



Bob T


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Fri 21, 2017 11:13 pm 
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Operation in series would be perfectly fine, try it with a second 120 added...


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 Post subject: Re: In Rush Current Limiter
PostPosted: Apr Sat 22, 2017 3:35 am 
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joybird wrote:
The Radio @ turn on @ 115 VAC draws 1.2 Amps settles down to .8 Amps running.
So would I be OK going with the CL90 2A or the CL80 3A?

With 0.8A running, you don't want a limiter rated at more than 3.2A. But is the 0.8A the true current? This set uses a half-wave rectifier so the line current is a combination of AC and DC. You need to use a true RMS meter that responds to both at the same time. Howver, hardly any of them do. As an alternative, you can measure the true RMS AC current and the DC current separately. Square each one and add them. Then take the square root of the sum. That is the actual current the radio draws. If you don't have a true RMS meter, you are out of luck. But you know the current is less than 2A since the fuses don't blow.

joybird wrote:
I like the idea of the larger size. Would the heat be the same small or large?

Probably not; it would depend on the resistance of the limiter at the current it is operating at. You can get a rough idea from the manufacturer's data sheet and use the power formula.

joybird wrote:
IWill Google the Ametherm. Any suggestions on that?
http://www.newark.com/ametherm/sl22-0r7 ... dp/72J6815
Very confusing to me as to ratings. Above one rated 12A so 1/4 of that is 3A. My MAX is 1.2A Would this one be suitable for the Radio?
115 VAC Max current Draw at turn on 1.2A running current .8A.

No, that one has too high a current rating.

joybird wrote:
YES Crazy Filament String. Yes @ 115 VAC it will blow 47 bulbs. Schematic insists on using #44 so put them in.
At Start up WOW do they get bright (12VAC seen) I am sure they would blow more easy if a Hot restart was done.
(QUICK OFF/ON) I have been careful bringing up Line Voltage with Variac.

Actually a hot restart wouldn't be any problem at all for the lamps. The tube heaters are hot so their resistance is high and the surge through the lamps would be small. Hot restarts are hard on the rectifiers, however.

joybird wrote:
Yes I would think the engineer I spoke with would have know better. I supplied all the info he wanted.
after all the Company makes these things , they should be more helpful.

Just about all the engineers who know what a tube is have retired. The guy you talked to only knows about switching power supplies, the main use for this product. If you called the other manufacturers of inrush limiters (there are a number of them), you wouldn't get any better answers.

joybird wrote:
6 #44 Lamps

You do know that not all the lamps are supposed to light at the same time? The band switch, S1, selects which to light. Here is a clearer schematic than the one posted above: http://www.nostalgiaair.org/pagesbymodel/393/M0014393.pdf. If they all light, there is a problem with this switch. Also note that there are resistors across these lamps; have you tested them?

Also another rule about using these devices: you can connect them in series but not in parallel. If you connect them in parallel, the one that heats up fastest will take all the load; they don't share well.

Good luck,

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Jim Mueller


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 Post subject: Re: In Rush Current Limiter
PostPosted: Apr Sat 22, 2017 12:04 pm 
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joybird wrote:
6 #44 Lamps

You do know that not all the lamps are supposed to light at the same time? The band switch, S1, selects which to light. Here is a clearer schematic than the one posted above: http://www.nostalgiaair.org/pagesbymode ... 014393.pdf. If they all light, there is a problem with this switch. Also note that there are resistors across these lamps; have you tested them?

Also another rule about using these devices: you can connect them in series but not in parallel. If you connect them in parallel, the one that heats up fastest will take all the load; they don't share well.

All resistors are New . Original I had 47 lamps installed and they were blowing. Found Note on Schematic that #44 needed
Have not blow any sine putting in #44

When I got this the Dial lamp harness was not existent. So Front Switch and Terminal Board for lighting wiring all new.

My best guess at the time
It took me quite a while to figure out how to wire it up.
Here is how it now lights
Band 4 (BC) All 6 lamps are ON
Band 3-1 Two Lamps on for each, Lighting just that portion of Dial

Did not know they worked in Series so if I use 2 of what I tried I will have 240 ohms at 1A. Or would it be at 2 Amps ?
Also does it matter which side of line they go in ?

Thanks
Bob T


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Sat 22, 2017 1:26 pm 
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Current would still be rated 1A...

For this radio I'd install the thermistor(s) in just the heater line(A or B connection), leave AC input to rectifier plate connected directly... This will eliminate the surges thermistor would see from rectifier charging the caps... You could install one in each A & B but I can't see any reason to do so... As far as initial surge at turn on, it won't make any difference whether rectifier plate is included or not, as tube isn't conducting when cathode is cold...


Tom


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Sat 22, 2017 2:11 pm 
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OK
I hooked up 2 of the 120 ohm 2A Limiters so gives me 240 ohms @ 2A in the "B" connection

Cold Start the Lamp Filament Voltage slowly goes up to 7.8 VAC and drops back to running @ 5.3 VAC

Hot Start even better Filament Volts go up to 6.5 VAC then back to 5.3 VAC

This is now with my full line Voltage of 122 VAC here.I have them in the B line

I think this would work out. What do you think Tom ?

The 220 ohm 1A are in the mail , should not make much difference
Schematic calls for 2 2A fuses. Would I be safer with 1A Even with a Hot start It never draws over .75 Amps
Set up as here with 122 Line

Bob T


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Sat 22, 2017 2:32 pm 
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Bob, I think what you have is fine, unless there is a issue mounting two thermistors I'd keep this configuration...

With the 220 surge should increase slightly, but who knows??? The thermistors I've measured in this range often have variance of 15-25 ohms between them...


Tom


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Sat 22, 2017 3:04 pm 
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No problem with 2, I have a open space on top center of chassis. I can put small Term Strip there. With HOT NOTE

But I will try the others when they arrive.

I am pleased with it now.

Thank you for the help, I was confused , the engineer made it more confusing, he must have not considered 11 tubes.
Regards,
Bob T


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 Post subject: Re: In Rush Current Limiter HELP Choosing
PostPosted: Apr Sat 22, 2017 6:41 pm 
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Sounds like a plan...

As far as fuses it no doubt had 2A specced because of large turn on surge... You could likely drop to 1A without issue, at worse you'll be replacing fuse... If it were to blow fuse, I'd go to 1½A...


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